Antenna for polarized propagation



Gicz) vJU Sept. 20, 1960 L. o. KRAUSE ANTENNA FOR POLARIZED PROPAGATION2 Sheets-Sheet 1 Filed June 4, 1958 HALF WAVELENGTH PHASE SHIFTER 5|TRANSMITTER 50 FIG. 2

FL 7 4 m 7 mm. mm M W HS EA mm A U Q N mm T 4 B C 6 N U J 0 @t f R m E TT T H I O M 2 w 56 N N A A R R TI TI FIG. 3

RESU LTA NT VECTOR VERTICAL VECTOR m T C E V E S w R TK mo m 0 L L FIG.4 BY M FIG. I

ATTORNEY Sept. 20, 1960 o. KRAUSE ANTENNA FOR POLARIZED PROPAGATION 2Sheets-Sheet 2 Filed June 4, 1958 90 PHASE DlFFERENCE 0 PHASE DIFFERENCEV444 VR FIG. 6

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I80 PHASE SHIFT 225 PHASE SHIFT HRZ INVENTOR. LLOYD 0. KRAU SE FIG.9

A TTORNE Y United States Patent C) ANTENNA FOR POLARIZED PROPAGATIONLloyd 0. Krause, North Syracuse, N.Y., assignor to General ElectricCompany, a corporation of New York Filed June 4, 1958, Ser. No. 739,748

12 Claims. (Cl. 343-895 This invention relates to antenna structures ofthe kind used for the radiation and reception of electromagnetic energyand more particularly to antenna systems for radiating and receivinghigh frequency energy having a broad azimuth directivity.

In many communication and television applications, there is a need forradiating electromagnetic energy from a central source to a plurality offixed or mobile receivers at any azimuth position about the centralsource. The radiation should be omnidirectional to permit the uniformdistribution of the radiant energy to all points in circles concentricwith the central source. Such a distribution affords the most efficientutilization of the available electromagnetic energy when the receiversare uniformly distributed over a given area or when the mobile receivershave equal probabilities of being at any position within the area.Unfortunately, many of the available communication antenna systems havelimited directivity. The radiation patterns of such antennas showdirections wherein the signal strength at particular azimuth angles isgreater than the signal strength at other azimuth angles. Therefore,mobile receivers may go between areas of low signal strength and areasof high signal strength thereby affecting proper operation of the mobilereceivers.

Although there are available communication antenna systems which aresubstantially omnidirectional, their radiation efiiciency is limited bythe spread in the elevation distribution of the electromagnetic energy.The elevation distribution may be defined as distribution in planesnormal to the surface of the earth. When communication antenna systemstransmit line of sight range signals, i.e., F.M. or television, most ofthe electromagnetic radiation transmitted in directions above thehorizon is incapable of reception and therefore wasted. To minimize theamount of unavailable radiation transmitted by such antenna systems, itis necessary to decrease the angular spread of the radiation elevationdistribution.

Many techniques employing complicated arrays and stacks have beenemployed in obtaining more desirable elevation directivitycharacteristics. The resultant antenna systems are usually complex andexpensive. However, a very satisfactory solution of the problem isobtained by using a helical antenna described and claimed in thecopending United States application of Lloyd 0. Krause and Howard G.Smith, Serial No. 732,482, filed May 2, 1958, as a continuation ofSerial No. 271,374, filed February 13, 1952, now abandoned, which isassigned to the same assignee. The above cited helical antenna is of theside fire type. However, the helical antenna, besides being of the sidefire type, radiates electromagnetic energy having its active componentpolarized normal to the antenna axis. Since a side fire antenna has aradiant energy flow normal to (radially from) the axis of the antenna,the vertical mounting of such an antenna yields the desiredomnidirectional radiation pattern. However, since the active component(electric field component) of the radiation is normal to the antennaaxis,

2,953,786 Patented Sept. 20, 1960 vertical mounting results in what isknown as horizontally polarized electromagnetic radiation. Horizontallypolarized radiation has many useful applications, for example, in thetransmission of television signals, but there are instances whenvertical or circular polarization are more desirable.

In the mobile communications art, vertically polarized radiation is lesssusceptible to certain types of interference. Therefore, many mobilesystems employ such radiation. Further, the vertical mounting of a whipantenna on a vehicle is much simpler than the mounting of a horizontalantenna. Vertically mounted antennas are highly sensitive to verticallypolarized electromagnetic radiation.

It is accordingly a general object of the invention to provide animproved antenna system.

It is a more specific object of the invention to provide an improvedantenna system which, while having broad azimuth distributioncharacteristics, has a desirable minimum of elevation distribution.

It is a more specific object of the invention to provide an antennasystem which has a high efficiency of radiation.

It is an object of one aspect of the invention to provide a highlyefiicient antenna system for radiating over a broad azimuth rangevertically polarized electromagnetic radiation.

It is another object of this aspect of the invention to provide animproved directional antenna system for radiating vertically polarizedelectromagnetic radiation.

Briefly, in accordance with a general aspect of the invention, anantenna system is provided which includes a linear conductor. A secondconductor is developed about the linear conductor in a given direction.The second conductor extends from a first point along the length of thelinear conductor toward a first of its ends. A third conductor is alsodeveloped in the same direction about the linear conductor. The thirdconductor extends from a second point along the length of the linear conductor towards its other end. The first point is disposed between thesecond point and the first end of the linear conductor. A firstenergization terminal is coupled to the linear conductor. Second andthird energization terminals are respectively coupled to the second andthird conductors (preferably but not necessarily at said first andsecond points respectively) for receiving signals to be radiated by thesecond and third conductors.

In accordance with a specific aspect of the invention, the azimuthorientation of the first and second points is predetermined. A signal isfed between the first and second energization terminals and the samesignal with a time phase relation is fed between the first and thirdenergization terminals so that the energy radiated from the second andthird conductors interacts to establish resultant vertically polarizedelectromagnetic radiation.

In some communication systems or in some military applications, it ishighly desirable to transmit first and second classes of informationsignals from an antenna system. It has been the usual practice toprovide an antenna system having separate antennas for radiating theenergy associated with the two classes of information. Attempts toradiate the energy associated with both classes of information oftenresult in interferences between the two signals.

Furthermore, to increase their versatility these systems often requirethat the electromagnetic radiation associated with each class ofinformation be transmitted in mutually orthogonal modes of polarization.That is, the radiation associated with the first class of signals bevertically polarized while the radiation associated with the secondclass of information be horizontally polarized.

It is, therefore, an object of a second specific aspect of the inventionto provide an antenna system which requires a single antenna structureto radiate the energy associated with two classes of informationsignals.

It is another object of this second specific aspect of the invention toprovide an antenna system which, while employing a single antennastructure, permits the radiation of electromagnetic energy associatedwith two classes of information within a minimum of mutual interference.

It is a further object of this aspect of the invention to provide anantenna system which permits the radiation of energy associated with twoclasses of information signals wherein the electromagnetic radiationassociated with one class of information is vertically polarized and theelectromagnetic radiation associated with the other class of informationis horizontally polarized.

Briefly, in accordance with this second aspect of the invention, theabove described antenna system is employed with a modified signalfeeding means. The signal feeding means permits the feeding of theinformation signals of the first class between the first and secondenergization terminals of the antenna system in a given time phase,while feeding the same information signals between the second and thirdenergization terminals in an out-ofphase relationship so that theresultant electromagnet radiation is vertically polarized. At the sametime the signal feeding means permits the feeding of the informationsignals of the second class between the first and second terminals in agiven time phase and feeding the same information signals in the sametime phase between the first and third energization terminals so thatthe resultant electromagnetic radiation associated with the second classof information signals is horizontally polarized.

It should be noted that such a system minimizes the interaction betweenthe electromagnetic radiation associated with the first and secondclasses of information signals when the operating frequencies associatedwith these information signals are different from each other.

Although linear polarization, whether horizontal or vertical, isdesirable in communication and military applications, there is often aneed for circularly polarized electromagnetic radiation. For example,circular polarization has been found particularly valuable in VHF FMcommunication systems and of possible value in television systems. Onereason is that linearly polarized electromagnetic radiation whenreflected changes polarization to some extent. Therefore, if thereceivers are surrounded by high objects which prevent line of sightreception, the electromagnetic radiation initially transmitted with apredetermined linear polarization may be received by a correspondinglyoriented antenna after reflection at a different polarization. However,when circularly polarized electromagnetic radiation is reflected thereis usually a strong enough linear component to ensure adequate receptionunder most conditions. It is therefore an object of another specificaspect of the invention to provide an improved antenna system forradiating circularly polarized energy.

It is another object of this aspect of the invention to provide animproved antenna system for radiating over a broad azimuth rangecircularly polarized electromagnetic energy.

It is a further object of this aspect of the invention to provide animproved omnidirectional antenna system for transmitting circularlypolarized electromagnetic radiation.

Briefly, in accordance with this third specific aspect of the invention,the antenna system of the second specific aspect of the inventionhandles a single kind of information signals. Thus, when the signalfeeding means feeds the information signals to the energizationterminals in the above described manner, there is an interaction betweenthe electromagnetic radiation transmitted from the second and thirdconductors. Since the antenna system is now radiating both horizontallyand vertically polarized radiation of the same frequency, the result ntp lariz t n will be circular when there is a ninety degree time phasedisplacement between the linearly polarized electromagnetic waves.

Additional objects, features and advantages of the invention will beapparent from the following detailed description when read with theaccompanying drawings in which:

Figure 1 shows an antenna structure which permits the radiation ofelectromagnetic energy with predetermined polarization in accordancewith a general aspect of the invention as determined by the signalfeeding means coupled to the antenna structure;

Figure 2 shows a signal feeding means for coupling to the antennastructure of Figure 1 to permit the radiation of vertically polarizedelectromagnetic energy in accordance with a specific aspect of theinvention;

Figure 3 shows a signal feeding means for coupling to the antennastructure of Figure 1 to permit the transmission of either crossedpolarized electromagnetic energy related to two classes of informationsignals or the transmission of circularly polarized electromagneticenergy related to a single information signal in accordance with furtheraspects of the invention;

Figure 4 is a vector diagram to show the interaction of theelectromagnetc radiation transmitted by the antenna structure of Figure1 when coupled to the feeding means of Figure 2 to establish avertically polarized electromagnetic wave;

Figure 5 is another vector diagram to show the vector interactionrequired to establish circularly polarized radiation;

Figures 6 to 9 are alternate vector diagrams using time as a parameterto show the vector interactions required to establish different forms ofpolarized energy. In particular, Figure 6 shows the. interaction whichproduces horizontal polarization; Figure 7 the interaction for circularpolarization; Figure 8 for vertical polarization; and Figure 9 forelliptically polarized radiation.

1. General description of helical antenna systems Helical antennasystems may be grouped into two characteristic types, side fire and endfire.

In the side fire type with which the subject application is concerned,the antenna system is vertically mounted with respect to the earth, andthe radiation pattern may be either linearly or circularly polarized.More exactly, the volumetric radiation pattern of the side fire type isa solid of revolution about the antenna axis of a directive lobe normalto the axis. The radiation from an end fire helical antenna system suchas is described and claimed in the copending United States applicationof 'Paul M. Pan, Serial No. 646,837 filed March 18, 1957, and assignedto the same assignee, is concentrated along the axis of the helicalantennas. The radiation may also be either circularly or linearlypolarized.

The side fire type is particularly useful in television broadcasting andin communication systems where receiving locations are in variousdirections. The end fire type is particularly useful for directedcommunications and in radar systems.

Side fire types may be arrayed; that is, a number of helical antennasmay be supported end to end along a common axis. The side fire typeswhen arrayed (stacked) produce a more concentrated radiation pattern indirections normal to the common axis.

Each helical antenna comprises a series of single turns or helices. Whenthe helical circumference is approximately some integral number ofoperating wavelengths, for example, two or four wavelengths, and isdriven between a point on the helix and a concentric conducting mast,the normal mode of radiation dominates; that is, the helical antenna isof the side fire type.

Each of the various embodiments of the invention has one majorcharacteristic in common; each comprises at least two radiatingconductors which are wound in the Same circumferential direction and inopposite axial directions about a concentric conductor and each of theradiating conductors has a separate feeding means.

II. Antenna system (Fig. 1)

A single bay system for radiating electromagnetic energy in which twohelical antennas are arranged coaxially about a concentric centralconductor is shown in Figure 1. It should be noted, however, that insome installations it may be desirable to axially stack several of thesingle bay systems to form a multi-bay system.

The system generally comprises a central conductor 20, which may alsoserve as a mast. The central conductor 20 is mounted on a support means(not shown) which may be a tower or the top of a high building. Aninsulator 21 sheaths the central conductor 20. A first energizationterminal 22, mounted in the insulator 21, insulatively extends throughthe central conductor 20 for connection to the inner conductor of thecoaxial line 32. A second energization terminal 24, mounted in theinsulator 21, also insulatively extends through the central conductor 20to connect to the inner conductor of the coaxial line 34. Each of theouter conductors of the coaxial lines 32 and 34 may be coupled to thecentral conductor 20 in a conventional manner. It should be noted,however, that these separate connections of the outer conductors areequivalent to a single connection to the central conductor 20, which ishereinafter termed a third energization terminal 26.

The energization terminals 22, 24 and 26, and the coaxial lines 32 and34 can be considered as a coupling system for coupling energy from anenergy source to the radiating conductors 42 and 44.

Insulating means, such as the insulator 21 or the equivalent, disposedabout the central conductor 20, support the radiating conductor 42 whichis connected to the first energization terminal 22 and the radiatingconductor 44, which is connected to the second energization terminal 24.The radiating conductors 42 and 44 are of the helical type whichrespectively extend in opposite axial directions from the energizationterminals 22 and 24.

In particular, the radiating conductor 42 and the radiating conductor 44are helical radiative conductors which extend in axially progressiveturns about a circular central conductor 20, which functions as aconductive support structure. The radiating conductor 42 is shown as aright-handed helix, that is, it is developed about the central conductor20 from its starting point opposite the energization terminal 22, in thesame manner as the threads of a right-handed screw. Similarly theradiating conductor 44 is a left-handed helix; that is, tracing it fromits starting point opposite the energization terminal 24, it follows apath similar to the path of threads of a left-handed screw.

The radiating conductors 42 and 44 each has an axial helical length(aperture) preferably in the range between one and one-half and fiveoperating wavelengths and a helix diameter and pitch such that thecircumference of each turn preferably equals an integral number ofoperating wavelengths. The radiating conductor 42, connected at one endto the energization terminal 22, winds in one direction around theinsulator 21 which encircles the central conductor 20. The radiatingconductor 44, which is connected at one end of the energization terminal24, winds in the same direction. The ends of each of the radiatingconductors 42 and 44 may be supported free or in contact with thecentral conductor 20.

The energization terminals 22 and 24 preferably have the same azimuthposition and arbitrary axial displacement so that the radiatingconductors 42 and 44 are symmetrical on either side of a plane locatedmidway between the energization terminals 22 and 24, and perpendicularto the axis of the central conductor 20. Such a symmetry permits theinteraction of the electromagnetic 6 energy radiated from each of theradiating conductors 42 and 44 to provide for controlled polarization ofthe resultant radiation.

Further, by providing equicircumferential turns each of an integralnumber of operating wavelengths, all points on the radiating conductors42 and 44 having the same azimuth direction radiate the same phase ofsignal. The electromagnetic radiation from these points interact witheach other to provide an equiazimuth distributed radially propagatedresultant electromagnetic wave which has a controlled elevationdistribution.

There is a relationship between the radial spacing between a radiatingconductor and central conductor and the length of the radiatingconductor. There is a further relationship between these two dimensionsand the helical pitch of the radiating conductors. In general, theradial spacing between a radiating conductor and central conductordetermines the characteristic impedance of the radiating system. Also,the smaller the spacing between the central conductor and a radiatingconductor, the smaller the radiation per unit length of radiatingconductor. Therefore, given a specific attenuation per unit length, itis possible to choose the length of the radiating conductor commensuratewith radial spacing to insure that any signal propagated along aradiating conductor is substantially completely attenuated upon reachingthe end remote from its energization terminal. Thus the termination ofradiating conductors 42 and 44 is neither important nor critical.

A further understanding of these relations may be obtained byconsidering the radiating conductors and the central conductor to formsections of a radiating transmission line. Electromagnetic energizationapplied between adjacent ends of the radiating conductors and thecentral conductor cause electromagnetic waves to travel along the lengthof the radiating conductors away from the points of energization. Inorder to constrain the propagation to travel in the helical pat-hinstead of the axial path as in a coaxial transmission line, thecoupling between a turn of the radiating conductor and the centralconductor must be greater than the coupling between adjacent turns ofthe radiating conductor. In general, the radiating conductor pitch isgreater than the radial spacing between the radial conductor and thecentral conductor. Furthermore, as the electromagnetic waves travelalong the radiating conductors, they gradually decay due to theradiation of the electromagnetic energy from the radiating conductors.Therefore, by making the radiating conductors of sufiicient length,reflections of electromagnetic waves from remote ends of the helicalconductors can be made substantially insignificant in effect. Typicalvalues for a specific case would be 0.1 operating wavelengths radialspacing, 2 operating Wavelengths per helical turn, .5 operatingwavelengths helical pitch, 5 turns per helix, with 20-26 decibels ofattenuation to the end.

Since the radiating conductors 42 and 44 and the central conductor 20can be considered as a pair of radiating transmission lines being fedfrom adjacent ends, the coaxial lines 32 and 34 are respectively coupledbetween the energization terminals 22 and 26 and 24 and 26 in thefollowing manner. The inner conductor of the coaxial line 32 is coupledvia the energization terminal 22 to the radiating conductor 42, whilethe outer conductor of the coaxial line 32 is coupled via theenergization terminal 26 to the central conductor 20 to provide afeeding means for the upper radiating transmission line which comprisesthe radiating conductor 42 and the central conductor 20. Similarly, theinner conductor of the coaxial line 34 is coupled via the energizationterminal 24 to the radiating conductor 44, While the outer conductor ofthe coaxial line 34 is coupled via the energization terminal 26 to thecentral conductor 20 to pro vide a feeding means for the lower radiatingtransmission 7 line which comprises the radiating conductor 44 and thecentral conductor 20.

The apparatus so far discussed provides an omnidirectional side fireantenna system. The polarization of the electromagnetic radiation isdependent on the signals (particularly their phasing) transmitted to thefeed means. Several types of linear and circular polarization areobtainable.

III. Generation of linearly polarized electromagnetic radiation Ingeneral, the electric field component of an electromagnetic waveradiated from a linear conductor is parallel to the length of the linearconductor and has an amplitude and direction related to the amplitudeand direction of signal current flowing in the linear conductor. As theelectromagnetic field radiates from the linear conductor, theorientations are maintained. Since incremental lengths of the radiatingconductors 42 and 44 may be considered as small linear conductors, theelectric field components associated with their radiation should have asimilar parallelity. Thus the electric field components should be linearand making an angle with the axis of the central conductor which is thesame as the pitch angle of the radiating conductors.

Electric field components have the property of interacting with eachother. They are vector quantities which are governed by the laws ofvector algebra. Since examples associated with these vector interactionsare hereinafter more fully described and shown, it will for the presentbe stated that when the electric field components radiated from theradiating conductors 42 and 44 have direction symmetry about thehorizontal plane, but opposite senses, they interact to produceresultant electric field components that are vertically polarized. Thestructural symmetry of the radiating conductors 42 and 44 ensure thatthe electric field components have directional symmetry. Their sense isdetermined by the instantaneous polarity of the signal current flowingin the radiating conductors. Thus, when there are opposite polarities ofsignal currents at corresponding points on the radiating conductors, theelectric field components will have opposite senses. To produce theopposite po- 'larity signal currents it is necessary to feed eachradiating conductor with the same signal but completely out of phase,i.e., one radiating conductor receives the signal and the otherradiating conductor receives the same signal, but one hundred and eightydegrees out of phase. In other words, the radiating conductors 42 and 44of Figure 1 are fed in push-pull.

Accordingly, Figure 2 shows apparatus for generating the desired out ofphase signals. The apparatus includes a transmitter 50 and a halfwavelength phase shifter 51. One output terminal of the transmitter 50is coupled via the coaxial line 55 to the half wavelength phase shifter51. The coaxial line 54 is coupled to another output terminal of thetransmitter 50, while the coaxial line 52 is coupled to the outputterminal of the half wavelength phase shifter 51. To transmit verticallypolarized electromagnetic radiation, it is only necessary to couplecoaxial lines 52 and 54 respectively to the colines 32 and 34 of Figure1.

Since transmitters and half wavelength phase shifters are well known inthe art, only their general requirements will be discussed. It should benoted that by using a conventional push-pull amplifier for the output ofthe transmitter 50, there is no need for a phase shifting circuit. If aphase shifting circuit is employed, it is necessary to ensure thatsignal attenuation of any consequence introduced by the phase shiftingcircuit, such as the half wavelength phase shifter 51, be compensated.One method is to introduce an attenuator at either end of the coaxialline 54. However, a more satisfactory means of compensation is to feed agreater amplitude signal to the coaxial line 55 than to the coaxial line54.

There has thus been shown means for generating out of phase signalswhich produce electric field components of opposite sense to yield aresultant electromagnetic field having vertical polarization, inaccordance with one embodiment of the invention.

When the electric field components are in the same direction and havethe same sense, the resultant radiation is horizontally polarized.Again, since the antenna system of Figure 1 will radiate electric fieldcomponents having the same direction, it is necessary to provide for asimilarity of sense. In other words, the polarities of the signals oncorresponding points of the radiating conductor must be the same. Inaccordance with another embodiment of the invention, to provide for thesame polarity it is necessary to feed the same signal without anyrelative phase shift (push-push) to each of the radiating conductors.

By providing predetermined relative phase shifts of the two signals fedto the antenna system of Figure 1, it is possible to produce radiationhaving a corresponding angle of polarization, in accordance with otherembodiments of the invention.

IV. Generation of crossed polarized electromagnetic radiation It hasbeen shown in section III that by feeding the radiating conductors inpush-pull, the resultant electromagnetic radiation is verticallypolarized and by feeding the radiating conductors in push-push, theresulting electromagnetic radiation is horizontally polarized.

If a first frequency signal is fed to the radiating conductors inpush-pull and a second frequency signal is fed to the radiatingconductors in push-push, crossed polarized electromagnetic radiation isradiated by the antenna system, i.e., there will be vertically polarizedradiation of the first frequency signal and horizontally polarizedradiation of the second frequency signal.

The first and second frequency signals may be fed alternately orsimultaneously. Simultaneous feeding permits the transmission of twoclasses of information from the same antenna system. A possibleapplication could be in television wherein the audio signals and thevideo signals might be simultaneously transmitted over differentcarriers.

There is little interaction of the two signals provided suitablediplexing means are used in the feed system.

Figure 3 shows apparatus for coupling to the antenna system of Figure 1for transmitting two cross polarized electromagnetic waves. Theapparatus includes first and second transmitters 60 and 62, a hybridjunction 64, and a quarter wavelength phase shifter 66. The transmitters60 and 62 are respectively coupled via the coaxial lines 68 and 70 tothe hybrid junction 64. A first output terminal of the hybrid junction64 is coupled via the coaxial line 74 to the coaxial line 34 (Fig. 1),and a second output terminal of the hybrid junction 64 is coupled viathe coaxial line 71, the quarter wavelength phase shifter 66, and thecoaxial line 72 to the coaxial line 32 (Fig. 1).

Each of the transmitters 60 and 62 may be of conventional design fortransmitting two forms of signal intelligence. The hybrid junction 64may be of the well-known ring variety, having the following properties:Signals received via the coaxial line 68 are transmitted in the samephase via the coaxial line 74 and via the coaxial line 71 lagging inphase by a quarter of an operating wavelength. Similarly, signalsreceived via the coaxial line 79 are transmitted in the same phase viathe coaxial line 71 and via the coaxial line 74 lagging in phase aquarter of an operating wavelength. The quarter wavelength phase shifter66 may be one of the many wellknown in the art. The basic function ofthe phase shifter 66 is the introduction of a lagging phase shift of aquarter of an operating wavelength in the signals received via thecoaxial line 71.

In operation, a signal is transmitted from transmitter 60 via thecoaxial line 68 to the hybrid junction 64. The hybrid junction 64transmits this signal without relative phase shift to the coaxial line74. The signal is also transmitted to the coaxial line 71 with a quarterof an operating wavelength phase delay. The delayed signal is furtherphase delayed another quarter of an operating wavelength by the quarterwavelength phase shifter 66. It is therefore transmitted via the coaxialline 72 to the coaxial line 32, phase-shifted half an operating wavelength. Since the signal on the coaxial line 74 has no phase shift andthe signal on the line 72 has a half an operating wavelength phaseshift, the signal from the transmitter 60 is fed to the antenna systemin push-pull and the resultant electromagnetic radiation is verticallypolarized.

At the same time, a signal is transmitted from the transmitter 62 viathe coaxial line 70 to the hybrid junction 64. This signal istransmitted from the hybrid junction to the coaxial line 71 withoutrelative phase shift and to the coaxial line 74 with a quarter of anoperating wavelength lagging phase shift. The quarter wavelength phaseshifter 66 introduces a quarter of an operating wavelength lagging phaseshift in the signal on the coaxial line 71 during its transmission tothe coaxial line 72. The signals from the transmitter 62 which are nowpresent on the coaxial lines 72 and 74, both have a phase delay of aquarter of an operating Wavelength and are therefore in phase with eachother. Thus, the signals from the transmitter 62 are fed to the antennasystem in push-push and the resultant electromagnetic radiation ishorizontally polarized.

It has therefore been shown that by using apparatus of Figure 3 to feedthe antenna system of Figure 1, it is possible to generate twoelectromagnetic waves that are crossed polarized, that is, oneelectromagnetic wave is horizontally polarized while the other isvertically polarized.

V. Generation of circularly polarized electromagnetic radiation As ishereinafter more fully described, there are three basic requirements forproducing circularly polarized electromagnetic radiation. There must bea vertically polarized electromagnetic wave and a horizontally polarizedelectromagnetic wave, both electromagnetic waves must have the sameoperating frequency and amplitude, and there must be a quarter of anoperating wavelength phase difference between the two electromagneticwaves.

In section IV there has been described apparatus for simultaneouslytransmitting horizontally and vertically polarized electromagneticwaves. By suitably modifying the apparatus of Figure 3, the remainingrequirements for producing circularly polarized electromagneticradiation are satisfied. First, the transmitters 60 and 62 must generatethe same signal. It may be more desirable to use a single transmittersuch as the transmitter 60, and feed both coaxial lines 68 and 70, inparallel. To ensure that equal amplitude signals are transmitted to theantenna system, it may be further necessary to introduce a conventionalattenuator in the coaxial line 74, to compensate any attenuation ofconsequence in phase-shifter 66. Additionally the antenna helix pitchangles must be suitably adjusted for equal horizontal and verticalcomponents. With these modifications, the electromagnetic radiation fromthe antenna system will be circularly polarized.

There has thus been shown apparatus for transmitting circularlypolarized omnidirectional electromagnetic radiation.

VI. Vector algebra Many physical quantities are best represented byvectors or directed line segments which both indicate magnitude anddirection. These physical quantities include forces, velocities, and theelectric field component of an electromagnetic wave.

Vectors may be added by means of several graphical methods. Figure 4shows the parallelogram method. A first vector 76 extends from a point75 While a second vector 78 also extends from the same point. A line 79is drawn from the arrowheaded tip of the vector 78 parallel to thevector 76. Another line 77 is drawn from the tip of the vector 76parallel to the vector 78 to form a parallelogram. The resultant vectoris the diagonal of this parallelogram drawn from the point 75 to point81.

The vectors shown in Figure 4 actually represent the electric fieldcomponents of the antenna system of Figure 1 when it is fed a sinusoidalsignal in push-pull. The points shown are for one cycle of thesinusoidal signal at thirty degree intervals. It should be noted at eachthirty degree point that the resultant vector is vertical. Thus theresultant of the electric field component of the electromagneticradiation is vertically polarized.

Figure 5 shows the vector addition which produces a rotating vector. Thecurve 82 which is disposed about the horizontal (X) axis 83 representsthe instantaneous magnitudes of a sinusoidally varying verticallydirected vector 84, while the curve 85 disposed about the vertical (Y)axis 86 represents the instantaneous magnitudes of a horizontallydirected vector 87. It should be noted from the angular coordinatesalong each axis that there is a ninety degree (quarter operatingwavelength) phase difference between the two vectors. It should befurther noted that the maximum amplitudes of both of the vectors 84 and87 are equal and their sinusoidal periods (frequency) are also the same.

At the beginning of the sinusoidal period (zero degrees), the verticallydirected vector whose amplitude is represented by the point 100 has Zeroamplitude while the horizontally directed vector 87 has a maximumpositive value (point 100'). The resultant vector 88a is shown on thecircle 90 as a line from the center 89 of the circle to the point -0.Consequently, the resultant electric vector is horizontal as indicated.

During the first quarter cycle, the vertically directed vector increasesin magnitude while the horizontally directed vector decreases inmagnitude and the resultant vector rotates. Its amplitude remainsconstant but its direction sweeps out ninety degrees of are on thecircle 90. The points 1011', 102-2 and 103-3 represent the resultantdirections respectively for the 30, 60 and 90 degree points in thesinusoidal cycle. The resultant vector 88b is the resultant at the 90degree point. It is basically the vertically directed vector 84, sinceat this point the horizontally directed vector has zero amplitude.During the second quarter cycle, the vertically directed vectordecreases in amplitude and the horizontally directed vector increases inamplitude in an opposite direction. The resultant vector sweeps outanother ninety degree are on the circle 90. For example, the vector 88represents the resultant of the vertically directed vector 84' and thehorizontally directed vector 87 at the degree point in the sinusoidalcycle. The process continues for the complete sinusoidal cycle and acomplete circle is traced out.

There is an alternate way of visualizing the interaction of the electricfield components radiated from the radiating conductors 42 and 44 (Fig.1). The radiating conductor 42 is a right-handed helix extending towardone end of the central conductor 20 and the radiating conductor 44 is aleft-handed helix extending toward the opposite end of the centralconductor 20. Incremental lengths of the radiating conductors radiateelectric field components that are parallel to their length. When thereis symmetry of the radiating conductors 42 and 44 about the horizontalplane which bisects the space between the energization terminals 22 and24, no relative time phase shift is introduced between the electricfield components radiated from the incremental lengths of the radiatingconductors 42 and 44 which are the same distance from their associatedenergization terminals. Since energy introduced at the energizationterminals 22 and 24 is radiated while traveling toward the ends of theradiating conductors 42 and 44, the direction of travel of energy alongthe incremental lengths determines the sense of the electric fieldcomponents.

Each of the incremental lengths makes an angle with the horizontalplane. Thus, the electric field component associated with eachincremental length makes a corresponding angle. Each of the electricfield components can be separated into a horizontal and a verticalcomponent. The sense of the horizontal components from each of theincremental lengths is the same, but the sense of the verticalcomponents is opposite. Thus, when viewed from a point external to theantenna system it appears that there is a relative hundred and eightdegree time phase shift introduced by the geometry of the helices on thevertical components but no time phase shift on the horizontalcomponents. It should be noted that this effective time phase shift ofthe vertical components is also introduced regardless of the relativetime phase relationship of the signals fed to the radiating conductors42 and 44 by the associated energization terminals 22 and 24.

Figures 6-9 have been provided to more clearly point out the interactionof the electric field components of the radiating conductors 42 and 44in terms of the time phase relationship of their horizontal and verticalcomponents and several examples will be given. Each of the examples usestime as the variable to control the relationship of equal amplitudevectors instead of physical direction as heretofore described in Figures4 and 5.

The vectors of Figs. 6-9 will be designated by an H" or V representingthe horizontal or the vertical component of the electric field componentradiated by the radiating conductors 42 and 44 followed by a numberindicating the radiating conductor. Thus, the vector H42 is thehorizontal component of the electric field component radiated by theradiating conductor 42.

Figure 6 shows the vector diagram of the electric field components whenthere is no time phase difference between signals transmitted from theenergization terminals 22 and 24. Since there is no time phasedifference, the vector H42 has the same direction as the vector H44.Since the vector V42 is in time phase with the vector H42 it issimilarly directed. However, the vector V44 is oppositely directedbecause of the effective one hundred eighty degree time phase shiftintroduced by the geometry of the helices. The vector HR is theresultant horizontal component and the vector VR is the resultantvertical component. It is seen that the horizontal component vectors H42and H44 and to produce a resultant of double amplitude and the verticalcomponent vectors subtract to yield a zero or null resultant. Thus, theelectric field for push-push feed is linear polarization in thehorizontal direction.

Figure 7 shows the vector diagrams when a ninety degree time phase shiftexists between equal amplitude signals fed from the energizationterminals 22 and 24. The vector H144 (the horizontal component of theelectric field component radiated by the radiating conductor 44) lags byninety degrees in time phase the vector H142 (the horizontal componentof the electric field component radiated by the radiating conductor 42).The vector V144 lags the vector V142 by two hundred and seventy degrees(ninety degrees from the time phasing introduced at the energizationterminals and one hundred and eighty de grees from the geometry of thehelices). The resultant vectors of the sumations of the horizontalcomponents is vector HRl and of the vertical components is vector VR1.Vectors HR1 and VR1 are ninety degrees out of time phase. Since theresultant vectors HRI and VR1 are of equal amplitude and in time phasequadrature, they 12 interact to produce circularly polarized radiation,as previously described. It should be noted, however, that if theoriginal horizontal and vertical components were of different amplitudesthe resultant polarization would be elliptical.

Figure 8 shows the vector diagram when the signals feeding theenergization terminals 22 and 24 are one hundred and eighty degrees outof time phase or push-pull. The vector H244 cancels the vector H242because of the phase opposition relationship. However, the vector V244reinforces the vector V242 because they are three hundred and sixtydegrees out of time phase or effectively in phase since the vector V244lags the vector V242 by one hundred and eighty degrees because of thetime phase shift introduced in the signals fed to the energizationterminals and lags another one hundred and eighty degrees because of thegeometry of the 'helices. The resultant electric field component istherefore vertically polarized, as heretofore described for push-pullfeed.

Figure 9 shows the vector diagram when the signals feeding theenergization terminals 22 and 24 are two hundred and twenty-five degreesout of time phase.

The vector H344 lags the vector H342 by this two hundred and twenty-fivedegrees, and the vector V344 lags the vector V342 by four hundred andfive degrees (two hundred and twenty-five degrees from the time phaseshift introduced by the feeding means and one hundred and eighty degreesfrom the helical geomery). The resultant vectors HR3 and VR3 are ofdifferent amplitude and ninety degrees out of time phase to yield anelliptically polarized electric field component. However, it should benoted that for unequal amplitudes of the horizontal and verticalcomponents the degree of ellipticity of polarization would be different.For example, for the case of Figure 9 with a 225 phase shift, areduction in the amplitude of the vertical component yields a lesselliptically polarized resultant.

In summary, it may be stated, that with equal amplitude components fortime phase differences other than multiples of ninety degrees thepolarization is elliptical. Circular polarization occurs for a ninetydegree phase difference. Linear polarization occurs when the time phasedifferences are multiples of one hundred and eighty degrees.

-It should be further noted that the above descriptions and explanationsare related to the interactions of the electric field components atpoints in a plane bisecting the junction of the two helices and normalto their collinear axes. At other elevation angles there will be anapparent increasing or decreasing phase shift between the upper andlower helices because of the differences in space phase delay.Therefore, circular polarization in the above-mentioned plane willbecome more elliptical at points elevationally displaced from thisplane.

VII. Conclusion There has thus been shown an improved omnidirectionalantenna system for efiiciently radiating electromagnetic waves havingpredetermined polarizations. One embodiment of the invention comprisesapparatus for transmitting omnidirectional vertically polarizedelectro-m'agnetic radiation. Further embodiments have been disclosed fortransmitting crossed polarized electromagnetic radiation representingtwo kinds of intelligence from the same antenna structure. The crossedpolarized radiation is transmittable over a broad azimuth range. Otherembodiments of the invention comprise apparatus for radiating linearlypolarized electromagnetic waves and apparatus for radiating circularlypolarized electromagnetic waves having an omnidirectional radiationpattern.

While a number of specific embodiments of the invention have beendescribed in detail, it should be apparent that many modifications andchanges may readily be t'nade without departing from the spirit andscope of the invention.

What is claimed is:

1. In combination, a first conductor, a second conductor developed in agiven direction about said first conductor and extending toward a firstend of said first conductor, a third conductor developed in the samegiven direction about said first conductor and extending toward theopposite end of said first conductor, a first energization terminalcoupled to said first conductor, a second energization terminalelectrically insulated from said first energization terminal and coupledto said second conductor, and a third energization terminal coupled tosaid third conductor.

2. The antenna system of claim 1 wherein said second and thirdconductors are helical radiative conductors.

3. A side fire antenna comprising a central conductor, a first radiativeconductor, said first radiative conductor being a right-handed helixdeveloped about said central conductor extending from a first pointalong the length of said central conductor toward one end of saidcentral conductor, a second radiative conductor, said second radiativeconductor being a left-handed helix developed about said centralconductor extending from a second point along the length of said centralconductor toward the other end of said central conductor, said firstpoint being disposed between said second point and said first end ofsaid central conductor, a first energization terminal coupled to saidfirst radiative conductor, a second energization terminal electricallyinsulated from said first energization terminal and coupled to saidsecond radiative conductor, a third energization terminal coupled tosaid central conductor, means for feeding a first kind of signal energyto said first and third energization terminals, and means for feeding asecond kind of signal energy to said second and third energizationterminals.

4. A side fire antenna comprising a central conductor, a first radiativeconductor, said first radiative conductor being a right-handed helixdeveloped about said central conductor and extending from a first pointalong the length of said central conductor toward a first end of saidcentral conductor, a second radiative conductor, said second radiativeconductor being a left-handed helix developed about said centralconductor and extending from a second point along the length of saidcentral conductor toward the second end of said central conductor, saidfirst point being disposed between said second point and the first endof said central conductor, each turn of each helix being an integralnumber or" operating wavelengths, first feeding means coupled to theportion of said first radiative conductor adjacent to said first point,and second feeding means electrically insulated from said first signalfeeding means and coupled to the portion of said second radiativeconductor adjacent to said second point whereby electromagnetic energyto be radiated travels along the length of said first and secondradiative conductors.

5. A side fire antenna to radiate electromagnetic radiation ofpredetermined polarization comprising a cylindrical conductor, a firstradiative conductor, said first radiative conductor being a right-handedhelix of given pitch developed about said cylindrical conductor andextending from a first point along the length of said cylindricalconductor and extending toward one end of said cylindrical conductor, asecond radiative conductor, said second radiative conductor being aleft-handed helix of the same given pitch developed about saidcylindrical conductor and extending from a second point along the lengthof said cylindrical conductor toward the other end of said cylindricalconductor, said first point being disposed between said second point andthe first end of said cylindrical conductor, each of the turns of eachof the helices of said radiative conductors having the same integralnumber of operating wavelengths, first feeding means coupled to theportion of said first radiative conductor adjacent to said first pointand adapted to feed signal energy to said first radiative conductor, anda second feeding means electrically insulated from said first signalfeeding means, said second signal feeding means being coupled to theportion of said radiative conductor adjacent said second point andadapted to feed signal energy to said second radiative conductor so thatthe electromagnetic radiation radiated by said first and secondradiative conductors interacts to produce a resultant electromagneticradiation having a predetermined polarization.

6. A side fire antenna to radiate electromagnetic radiation ofpredetermined polarization comprising a central conductor, a firstradiative conductor, said first radiative conductor being a right-handedhelix of given pitch developed about said central conductor andextending from a first point toward one end of said central conductor, asecond radiative conductor, said second radiative conductor being aleft-handed helix of the same given pitch developed about said centralconductor and extending from a second point along the length of saidcentral conductor toward the other end of said central conductor, saidfirst point being disposed between said second point and the first endof said central conductor, each of the turns of each of the helices ofsaid radiative conductors having the same integral number of operatingwavelengths, a signal source, first signal feeding means responsive tosaid signal source for feeding signal energy to the portion of saidfirst radiative conductor adjacent to said first point, and secondsignal feeding means responsive to said signal source for feeding signalenergy to the portion of said second radiative conductor adjacent tosaid second point in a relative time phase displacement with respect tothe signal energy fed from said first signal feeding means so that theelectromagnetic radiation radiated by said first and second radiativeconductors interacts to produce a resultant electromagnetic radiationthat is vertically polarized.

7. A radiating system to radiate electromagnetic radiation ofpredetermined polarization comprising a central conductor, a firstradiative conductor, said first radiative conductor being a right-handedhelix of given pitch developed about said central conductor toward afirst end of said central conductor, a second radiative conductor, saidsecond radiative conductor being a lefthanded helix of the same givenpitch extending from a second point along the length of said centralconductor toward the other end, each of the turns of each of the helicesof said radiative conductors having the same integral number ofoperating wavelengths, said first point being disposed between saidsecond point and said first end of said central conductor, first feedingmeans coupled to the portion of said first radiative conductor adjacentto said first point and adapted to feed signal energy to said firstradiative conductor, a second signal feeding means coupled to a portionof said second radiative conductor adjacent to said second point andadapted to feed signal energy to said second radiative conductor, atransmitter, and a half wavelength phase shifter, said transmitter beingcoupled to said first feeding means, and to said second signal feedingmeans via said half wavelength phase shifter, so that theelectromagnetic radiation radiated from said first and second radiativeconductors interacts to produce resultant vertically polarizedelectromagnetic radiations.

8. A side fire antenna system to radiate electromagnetic radiation ofpredetermined polarization comprising a central conductor, a firstradiative conductor, said first radiative conductor being a right-handedhelix of given pitch developed about said central conductor andextending from a first point toward a first end of said centralconductor, a second radiative conductor, said second radiative conductorbeing a left-handed helix of the same given pitch extending from asecond point along the length of said central conductor towards theother end, each of the turns of each of the helices of said radiativeconductors having the same integral number of operating wavelengths,said first point being disposed between said second point and said firstend of said central conductor, first feeding means coupled to theportion of said first radiative conductor adjacent to said first pointfor feeding signal energy to said first radiative conductor, a secondsignal feeding means coupled to the portion of said second radiativeconductor adjacent to said second point for feeding signal energy tosaid second radiative conductor, a first signal source of signal energyof a first frequency, a second signal source of signal energy of asecond frequency, and coupling means for coupling said first and secondsignal sources to said first and second signal feeding means whereby theelectromagnetic radiation radiated by said first and second radiativeconductors interacts to produce resultant electromagnetic radiationshaving predetermined polarizations.

9. The apparatus of claim 8 wherein said coupling means couples signalenergy from said first signal source to said first signal feeding meansand in the same time phase to said second signal feeding means toproduce an electromagnetic radiation having a horizontal polarizationand said coupling means couples signal energy from said second signalsource to said first signal feeding means and the same signal energy intime phase opposition to said second signal feeding means to producevertically polarized electromagnetic radiation.

10. A radiating system to radiate electromagnetic radiation ofpredetermined polarization comprising a central conductor, a firstradiative conductor, said first radiative conductor being a right-handedhelix of given pitch developed about said central conductor extendingfrom a first point toward a first end of said central conductor, asecond radiative conductor, said second radiative conduotor being aleft-handed helix of the same given pitch extending from a second pointalong the length of said central conductor toward the other end, each ofthe turns of each of the helices of said radiative conductors having thesame integral number of operating wavelengths, said first point beingdisposed between said second point and said first end of said centralconductor, first feeding means coupled to the portion of said firstradiative conductor adjacent to said first point for feeding signalenergy to said first radiative conductor, second signal feeding meanscoupled to a portion of said second radiative conductor adjacent to saidsecond point for feeding signal energy to said second radiativeconductor, a transmitter, junction means, means for coupling saidtransmitter to said junction means, and means for coupling said junctionmeans to said first signal feeding means and said second signal feedingmeans so that the electromagnetic radia- 16 tion radiated from saidfirst and second radiative conductors interacts to produce resultantcircularly polarized electromagnetic radiations.

11. A radiating system to radiate electromagnetic radiation ofpredetermined polarization comprising a central conductor, a firstradiative conductor, said first radiative conductor being a right-handedhelix of given pitch developed about said central conductor extendingfrom a first point toward a firs-t end of said central conductor, asecond radiative conductor, said second radiative con-' ductor being aleft-handed helix of the same given pitch extending from a second pointalong the length of said central conductor toward the other end, each ofthe turns of each of the helices of saidradiative conductors having thesame integral number of operating wavelengths, said first point beingdisposed between said second point and said first end of said centralconductor, first feeding means coupled to the portion of said firstradiative conductor adjacent to said first point for feeding signalenergy to said first radiative conductor, second signal feeding meanscoupled to a portion of said second radiative conductor adjacent to saidsecond point for feeding signal energy to said second radiativeconductor, first and second transmitters, junction means, phase shiftingmeans, and means for coupling said first and second transmitters to saidfirst feeding means via said junction means and to said second feedingmeans via said junction means and said phase shifting means, so thatsignals from said first transmitter are radiated from said first andsecond conductors with a given polarization and signals from said secondtransmitter are radiated from said first and second conductors with apolarization different from said given polarization.

12. The radiating system of claim 11 wherein said phase shifting meansis a quarter wavelength phase shifter and said signals from said firstand second transmitters are radiated with horizontal and verticalpolarizations respectively.

References Cited in the file of this patent UNITED STATES PATENTS2,619,635 Chait Nov. 25, 1952 FOREIGN PATENTS 724,795 Great Britain Feb.23, 1955 OTHER REFERENCES (Pub. 1) Electronics, Ground-to-Air AntennaUses Helical Array, March 1956, pp. 161-463.

(Pub. II) Electronics, Sidefire Helix VHF-TV Transmitting Antenna,August 1951, vol. 24, pp. 107409.

